RECENT RESEARCH HAS NOW ESTABLISHED that thinking too much can rot the brain. What they have yet to discover is that meditation is the key to the "off" button.

The Economist puts it perfectly: "Just as hard labor leaves marks on the hands, hard thinking leaves marks on the brain."

And medical research has known for some time that the brain is a malleable organ: the brains of sportsmen look different from computer users.

In the 1960's, research at University of California at Berkeley showed that rats brought up in a stimulating environment had denser, more complex brains than those in boring environments. Even old rats put in a more interesting cage show the same changes in their brains, with more synaptic connections between the cells supporting the old adage of "use it or lose it."

Not only do the brain cells increase, but the blood supply which brings the needed energy sources increase too. So, not only do "young interested rats develop 20-25 more synapses per nerve cell than do their bored contemporaries," but also they have "80% more capillaries" to supply the energy-bearing blood.

Recent research by William Greenough and his colleagues at the University of Illinois at Urbana-Champaign subjected three sets of rats --"acrobats," "jocks," and "couch potatoes" to different environments--with the acrobats challenged by tasks that required coordination, the jocks just challenged physically, and the couch potatoes not challenged at all. The acrobats showed dramatic changes to the parts of the brain involved with coordination.

But what about overdoing it? It is also known that thinking too much can kill brain cells. It appears that chemicals excreted by thinking cells may not be cleared away quickly enough and may poison and kill the brain cells.

When Ruben Gur at the University of Pennsylvania in Philadelphia asked men he was studying to relax, they could not -- their brains kept banging away at whatever they had been doing before without their being aware of it. Essentially this means, like all non-meditators, they were unaware of their thinking.

By contrast, women shifted to thinking about something completely different, using a different part of their brain. This difference, he believes, may explain his other main finding, which is that men's brains rot a lot faster than women's. Despite their big head start, by the age of 45, with their attention span and memory failing, the front of the men's brains which is responsible for "complex thinking" has shrunk to same size as "the frontal lobes of women of the same age." Alzheimer Lite all round for the boys.

So, not surprisingly, the brain works very much like the rest of our biological system. Rest between periods of exertion -- is the natural way of functioning. Lack of rest will cause over-training in athletes and reduce their function...the same is obviously true of the brain. And there is an intriguing relationship between awareness of breath and the fatigue that precedes heart attacks in stressed patients, over-training in athletes, and the chronic fatigue syndrome in others.... And while at least the athletes muscles rest while he or she sleeps, our multimedia brains do not. They switch over to a picture show called dreams, which in stressed, tense people can be quite a horror show.

Similarly it is not surprising that other investigators are increasingly recognizing a connection between alertness and function on the one hand, and relaxation on the other.

The key to reducing brain loss with age is the ability to relax the brain -- which means allowing the mind to stop and rest. The first essential step is to become aware of our thoughts. This is the knack of meditation. Then you can experience a real surprise. Thoughts are very shy. The moment you become aware of them, they begin to dissolve, leaving behind, "the peace that passeth all understanding."